Due Wed
23rd -- 9:00
5:00 AM
PM
Mon Sep 19th
Please use homework cover sheet.
This is an INDIVIDUAL homework set.
This is an INDIVIDUAL homework set.
4) [10 pts] Answer both of the following short essay questions.
a) [5 pts] A coworker questions the calculations you performed when converting Z12, Z13 and Z23 to Z1, Z2 and Z3
for a 3-winding transformer. He says that since Z2 is negative, you've made a mistake. What do you tell him
(be polite)?
b) [5 pts] A conceptual phase-shifting transformer is used in positive and negative sequence networks to represent
the phase shift of the phase A voltages and currents from one side to the other. Ratios like 1/30E or 1/-30E are
common. What effect do these phase shifting transformers have if you want to transfer an impedance from one
side to the other?
5) [15 pts] A new 3φ transformer has the following self-cooled (OA or ONAN) ratings:
Primary: Y-connected, 345 kV, 296 MVA
Secondary: Y-connected, 118 kV, 296 MVA
Tertiary: Δ-connected, 13.8 kV, 77 MVA
Binary short-circuit tests performed at the factory give the following results:
Z12 = 6.21% on 296-MVA 345-kV base.
Z13 = 55.9% on 77-MVA 118-kV base.
Z23 = 42.1% on 77-MVA 13.8-kV base.
Find the per unit impedances Z1, Z2 and Z3 on a base of 100 MVA, 118 kV. These must be provided to your systems
studies engineers. It may be helpful to refer to section 2.8 of your text book.